In current franking machines, the electronic equipment is organized in conventional manner about a program-controlled microprocessor. The microprocessor updates, in particular, one or more non-volatile memories assigned to recording the total value of franking operations performed, and also, at least in pre-payment franking machines, the values of successive amounts of credit loaded into the machine together with the amount of credit remaining available in the machine. The non-volatile memory which records these accounts is referred to as the machine meter memory or as the machine state memory.
Given the amount of money represented by each franking machine and even more so the amount of money represented by all franking machines in operation, it is essential that such machines should include sufficient redundancy and checking to be able to detect any kind of anomalous operation.
One simple and well-known means for this purpose consists in providing two non-volatile memories and recording the machine meter state twice over in separate manner. If a difference is detected between the contents of the two memories, then the machine is put into a fault state. The machine locks up and further franking becomes impossible.
In the event of a fault caused by a breakdown or failure of the components in the electronic equipment or due to an attempted fraud, it is necessary to rediscover the meter state prior to the occurrence of the fault. To this end, the meter state is recorded in each memory with a large amount of redundancy. In particular, a record is made in each non-volatile memory of the up meter which gives the total value of all franking operations performed, the down meter which gives the remaining amount of credit available, and the cumulative meter which gives the total amount of credit successively loaded into the machine, thereby enabling arithmetic checks to be performed between these three meters. Often, each of these three meters is associated with an error detection code related to the state of each meter and recorded therewith in each memory. Such redundancy shows up a faulty memory. The same redundancy can also be used in a non-negligible number of cases to conclude that the machine is not at fault and also that there has been no attempt at fraud, but simply that the memories have fallen out of step with each other, which can be rectified fairly simply. The operation of the machine may have been disturbed by transient disturbances from various possible origins, e.g. electromagnetic or electrostatic origins, etc.
A test procedure is provided for rediscovering the state of the meter prior to the appearance of the fault and also, possibly, for diagnosing that the memories have merely fallen out of step. The test procedure is performed in the presence of the user and of a representative of the postal service. The franking machine which was initially sealed is unsealed in order to gain access to the non-volatile memories.
During this test procedure, a device called a test tool is used to read the contents of the memories, to compare the contents in order to show up differnces, and to verify redundancies so as to show up a memory that is faulty, if any. In general, the test tool is fitted with a test connector which is connected thereto by a cord, and the franking machine is fitted with an internal connector complementary to the test connector and connected in parallel on the links between the access terminals of the memories and the access terminals of the electronic equipment, and in particular of the microprocessor.
The test tool thus gains access to the memories by having its test connector connected to the complementary connector provided for the purpose in the machine and made available when the machine is unsealed.
In theory, such access to non-volatile memories is simple. However, it requires isolating resistances to be included in the links between the memories and the electronic equipment. These isolating resistances are there to prevent a possibly faulty portion of the electronic equipment from imposing a wrong voltage level on the links, e.g. a high level or a low level such as ground. The resistances must also make it possible to read the non-volatile memories even if the machine is not powered, for example if its power supply has broken down. Under such conditions, the test tool injects current into the resistances such that if these resistances are connected to a low level on the electronic equipment side they are raised to a sufficiently high level on the memory side to allow the memories to operate properly.
The object of the present invention is to avoid the constraints and drawbacks related to such coupling between the non-volatile memories and the electronic equipment, and also between the non-volatile memories and the test too, while making it possible to obtain selective coupling between the memories and the electronic equipment or the test tool.